Electrochemical conversion of CO 2 to syngas with a wide range of CO/H 2 ratio over Ni/Fe binary single-atom catalysts
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partment of Chemistry, School of Science, Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin 300072, China 2 Institute of Energy, Hefei Comprehensive National Science Center, Hefei 230000, China 3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China § Meng Zhang and Zheng Hu contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 28 June 2020 / Revised: 15 July 2020 / Accepted: 15 July 2020
ABSTRACT A series of carbon-based binary single-atom catalysts of Fe and Ni coordinated by nitrogen are fabricated using a glucose-chelating method. Depending on the Ni/Fe content, they exhibit a wide-range of controllable CO/H2 ratio from 0.14 to 10.86, which is meaningful to specific chemical processes. The durability of the catalyst is evaluated over an 8-hour period with no significant degradation of activity. The variation of the faradaic efficiency with Ni/Fe content is justified by density-functional-theory based calculation of the reaction barrier in both hydrogen evolution and CO2 reduction reactions.
KEYWORDS CO2 reduction, syngas, binary single-atom catalyst, electrocatalysis
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Introduction
Synthesis gas (syngas), the gas mixture of carbon monoxide (CO) and hydrogen (H2), is a highly desirable feedstock for the production of various hydrocarbons through the FischerTropsch synthesis [1]. In practical applications, the specific proportion of CO/H2 in syngas is crucial for maximizing the product yield [2]. Conventionally, tunable syngas production predominantly relies on two mature technologies, coal gasification and natural gas reforming [3]. The harsh conditions required for synthesis and the dependence on non-renewable fossil fuels have prompted researchers to explore new environmentally friendly techniques for tunable syngas production [4, 5]. Owing to the abundance, low cost and nontoxicity, CO2 and water can be regarded as ideal chemical feedstock for the synthesis of syngas [6–8]. Given the combination of CO2 reduction and water splitting, the electrochemical reduction of CO2 and H2O can convert them to syngas and value-added chemical feedstocks by utilizing off-peak electricity or intermittent renewable energy sources, signifying a green way for energy storage and carbon recycling [9–13]. Moreover, the electrochemical reduction of CO2 for syngas synthesis is performed under ambient reaction conditions [14–17]. However, since the linear molecule of CO2 is extremely stable, the CO2 reduction reaction (CO2RR) is kinetically sluggish and requires a high conversion overpotential, which results in low activity and Faradaic efficiency (FE). In addition, the simultaneous hydrogen evolution reaction (HER) in the aqueous electrolyte under cathodic polarization is unavoidable during CO2RR [18]. Therefore, it is of great significance to explore the rational design and synthesis of CO2RR electrocatalysts to regulate the CO2RR and HE
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